Paddlefish’s doubled genome may question theories on limb evolution

The American paddlefish — known for its bizarre, protruding snout and eggs harvested for caviar — duplicated its entire genome about 42 million years ago, according to a new study published in the journal Genome Biology and Evolution. This finding may add a new twist to the way scientists study how fins evolved into limbs since the paddlefish is often used as a proxy for a more representative ancestor shared by humans and fishes.

“We found that paddlefish have had their own genome duplication,” said Karen Crow, assistant professor of biology at San Francisco State University. “This creates extra genetic material that adds complexity to comparative studies. It may change the way we interpret studies on limb development.”

In order to study how human limbs develop, scientists compare the limb-building genes found in mice with fin-building genes found in fishes. Previous research on paddlefish has suggested that fishes possessed the genetic toolkit required to grow limbs long before the evolution of the four-limbed creatures (tetrapods) that developed into reptiles, birds, amphibians and mammals.

In the last decade, paddlefish have become a useful benchmark in evolutionary studies because their position on the evolutionary tree makes them a reasonably good proxy for the ancestor of the bony fishes that evolved into tetrapods such as humans. However, the fact that paddlefish underwent a genome duplication could complicate what its genes tell us about the fin-to-limb transition, says Crow.